[U-Boot] Intialisation of Interrupts

[Graeme Russ]

On 09/09/11 18:51, Flash K wrote:
> Hi Graeme,
> 
> I was going through the U-boot code. Could you please help me with the
> following? I wanted to know as to where the CPU interrupts are initialised.

look in arch/x86/lib/board.c for init_sequence_f and init_sequence_r -
These arrays show the init sequence for pre-relocated U-Boot and relocated
U-Boot respectively.

Now interrupts are a bit tricky - interrupt_init() which is called directly
in the post-relocation sequence actually initialises the programmable
interrupt controller (PIC). CPU level interrupts (exceptions etc) are
actually initialised in cpu_init_r() - For a stock x86 build, this is
actually aliased to x86_cpu_init_r() which you will find in arch/x86/cpu/cpu.c

So the IDT (Interrupt Descriptor Table) is actually initialised immediately
after relocation and then the PIC a little later on. Once the IDT is
loaded, CPU exceptions can be handled and after the PIC is initialised,
external interrupts (from devices) can be handled.

> I believe it should be along with the CPU initialisation and before the

Yes, it is

> northbridge and southbridge intialisation. I wanted to implement a logic to

Well, currently the x86 port has no concept of North and South bridges. For
 such a system, the Northbridge may contain the SDRAM controller and may
need to be initialised (at least partially) first

> read the state of a GPIO pin and carry out some action based on this key
> press. I want to do this before the Bootloader is invoked.

board_early_init_f and board_early_init_r are you best bets to put this
kind of logic. board_early_init_f is extremely early - You may not have
GPIO set up (unless it sets it up). board_early_init_r is called just after
the CPU interrupts are enabled but before the PIC has been configured

Regards,

Graeme